The present invention relates to an image processing system and, more particularly, to an image processing system which includes an image memory and a control computer and which effectively performs data access at high speed between the image memory and control computer.
An image memory in an image processing system is generally regarded as an external peripheral component with respect to the control computer. Therefore, an interface is arranged between the image memory and the control computer via a data bus. The data is read out from the image memory always through the interface. In order to read out image data from the image memory and fetch it in the control computer or write image data in a desired memory area of the image memory, a series of steps of various operations must be performed. For example, data transfer control through the data bus must be performed. Mode designation data which indicates the mode of the interface, and the data to be stored must be properly selected. Furthermore, a read/write signal must be properly controlled. The data access control for the image memory which includes various types of control operations and/or data selection with respect to the interface must be repeated every time data access of the image memory in the image processing system is performed. Therefore, the data access procedure is very cumbersome, and a total access operation is undesirably time consuming. The interface of the image processing system is connected to a number of peripheral devices such as a data input unit, a display unit, a hard copy unit and the like, besides the image memory. Data access cannot be performed while the interface is being operated for any peripheral device other than the image memory. In other words, data access may only be performed while the interface is in the ready state. Therefore, the long total access time including the access time which is required to perform cumbersome procedures including the various operations described above, results in a drawback, preventing effective image processing.
In this manner, according to the conventional image processing system, before data transfer between the control computer and the image memory it must be checked whether or not the interface is in the ready state and whether or not a device is available to receive data. When data to be read out from a memory area of the image memory corresponds to a given screen area of the display unit, and data is subsequently displayed in accordance with raster scanning, the conditions of the interface and of the device which receives data do not present a major problem. However, when the operator wishes to randomly access data of a large number of pixels many times among those pixels the data of which is stored in the image memory, access control time is greatly increased, thus degrading the efficiency of the image processing operation, and hence entailing a distinct problem.